The present application relates to vacuum boosters and, more particularly, to variable output force rate brake system vacuum boosters.
Modern automotive braking systems typically include a vacuum booster capable of magnifying the brake input force supplied from the brake pedal. Vacuum boosters typically utilize the vacuum created by the engine, or a separate vacuum source, to create a pressure differential within the booster that in turn creates the desired force gain. The force gain of a vacuum booster may be defined as the magnitude of the output force created by the vacuum booster per unit of input force from the brake pedal.
Traditionally, the force gain has been constant throughout the normal range of use. However, there is now a desire to provide additional safety functionality to the brake system by creating a larger force gain after a predetermined threshold input force value has been reached, as shown in FIG. 1. Specifically, a higher force gain characteristic in the upper range of pedal input force will allow the brake system to provide the vehicle driver with the ability to achieve greater deceleration capability relative to a standard single gain vacuum booster.
Accordingly, there is a need for a vacuum booster capable of generating a variable output force gain without affecting the normal operating range of the vacuum booster and only under conditions requiring high output force, such that the vacuum booster operates generally seamlessly to drivers.